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Catch the join bug in a churn query before it ships

Practice: Catching mistakes and made-up facts. About 5 minutes.

About this exercise

An analyst's query claims to show the share of September signups that never created a project, but it can only return 0%. Write exactly 2 numbered lines labeled Problem: and Effect:, each under 20 words, then put only the corrected FROM/JOIN line in one code block. Keep the rest of the query unchanged. Under 50 words outside the code.

Common mistakes when you ask AI for this

  • Rewriting everything. The AI hands back a whole new query, which Dev has to diff line by line. Try: Add: "Only the corrected FROM/JOIN line in the code block."
  • Not asking for the cause. The AI fixes it silently or writes paragraphs on join types. Try: Add: "2 numbered lines labeled Problem: and Effect:, under 20 words each."
  • Letting the claim stand. The AI may repeat Dev's conclusion without saying the 0% is impossible. Try: Add: "Say what the 0% result really means."
  • Getting a tutorial. By default the AI explains every part of the code at length, which you then have to scroll past. Try: Add: "After the code, one line under 20 words. Nothing else."

What a strong prompt includes

  • Asks for the cause
  • Asks about the result
  • Limits the fix to one line
  • Sets the shape

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